ABSTRACT (Environmental Science and Engineering) Research Project 3 Per- and polyfluoroalkyl substances (PFAS) are chemicals that are of emerging concern because they are widely released into the environment where they tend to be persistent and bioaccumulative. Some PFAS are associated with adverse health outcomes in people, and production of a limited number of them (e.g., PFOA and PFOS) has been phased out due to these concerns. However, there are approximately 5,000 PFAS, and there is considerable uncertainty regarding the human health and environmental safety of these compounds because most PFAS have never been tested. Because these compounds are routinely released into waterways that serve as sources of drinking water and nutrition via consumption of fish and aquatic wildlife, there is an immediate need to better understand their environmental fate and effects. As concerns about PFAS in the environment are beginning to grow, there are increasing reports of the presence of these compounds in water and in aquatic organisms, but our understanding of their bioaccumulation potential and toxicity to aquatic life is limited. This project specifically addresses concerns about the bioaccumulation and toxicity of PFAS in aquatic food webs. One major goal of this project is to compare the accumulation of PFAS (12 different compounds) in a food web context by comparing aqueous uptake in primary producers (periphyton), primary consumers (mayflies), and secondary consumers (zebrafish) in the laboratory. A second major goal is to understand the potential for different compounds to move trophically in food webs by measuring the movement of different compounds from periphyton to mayflies to fish. Only by doing controlled studies in the laboratory can we systematically understand the bioaccumulation dynamics of these different compounds based on their different chemical structures. The next major goal of this work is to compare the toxicity of different PFAS to zebrafish. While zebrafish is a recognized model for human health studies, this project utilizes the deep understanding of this species' biology to explore the consequences of PFAS exposure to fish. The project will compare the toxicity of 12 different compounds in zebrafish using traditional toxicity approaches (exposures from water) but will be unique in that it will also assess the potential for dietary PFAS exposures to contribute to toxicity because in nature, exposures are likely to both PFAS in water and in the diet. Finally, these laboratory studies will be complemented by field investigations of PFAS in local waterways and in the tissues of aquatic fish and wildlife. This work is prompted by local contamination of a major watershed by a PFAS manufacturing plant and associated concerns about real-world exposures. Specifically, the project will measure PFAS in fish and wildlife (alligators) that are potential dietary exposure routes of these contaminants to people. Together, the project will provide much needed information about the bioaccumulation, toxicity, and exposure profiles of PFAS in the aquatic environment.